Cosmic cats and nuclear blasts: the strange history of interstellar messages

So you’ve received a message from an extraterrestrial intelligence. Congratulations! You are now at the centre of one of the most important events in human history. But now comes the hard part: what do you say in return – and, more importantly, how do you say it?

For the past 200 years, the problem of interstellar communication with an extraterrestrial intelligence has vexed some of the world’s greatest scientists and mathematicians. Carl Friedrich Gauss, the mathematician and inventor of the heliotrope, suggested using a large array of mirrors; Guglielmo Marconi and Nikola Tesla, pioneers of wireless communication, found a solution in radio waves; and John McCarthy and Marvin Minsky, the progenitors of artificial intelligence, wanted to send computers into space as our extraterrestrial envoys.

Any solution to the problem of interstellar communication comes laden with assumptions about the nature of extraterrestrial intelligence and inevitably reflects the technological sophistication of the era.

The problem, briefly stated, is how to design a message that can be understood by an extraterrestrial intelligence about which you can know nothing with absolute certainty.

This turns the design of interstellar messages into an exercise in identifying universals that can be presumed to be recognised by any entity endowed with higher intelligence. It is, in other words, the search for what may be called a language of the universe.

As Galileo recognised in The Assayer, his foundational treatise on the scientific method, “this grand book, the universe, stands continually open to our gaze. It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures without which it is humanly impossible to understand a single word of it.”

Following Galileo’s lead, most systems designed for interstellar communication have been rooted in mathematics on the grounds that it would be understood by any intelligent extraterrestrials. But how does one discuss maths with an extraterrestrial?

By the mid-19th century, scientists and mathematicians in Europe began to seriously consider methods for communicating with extraterrestrials that they believed might inhabit the moon and Mars. The first such system is attributed to Gauss, who developed a scheme “to get in touch with our neighbours on the moon” that involved creating a massive visual proof of the Pythagorean theorem in the Siberian tundra.

This visual proof was to consist of a right triangle bordered on each side by squares and would be created by planting rows of trees for the borders and filling the interior of the space with wheat.

Gauss’s proposal appears to have influenced the Austrian astronomer Joseph Johann von Littrow, who later advanced his own plan for establishing contact with our lunar neighbours. His design involved digging trenches in the Sahara in various geometric shapes, filling the trenches with water, topping them with kerosene, and then setting them alight to send flaming messages to the moon.

For better or worse, neither of these outlandish schemes for extraterrestrial communication came to fruition. But another of Gauss’s proposals did exert a lasting influence on early European ideas for contacting extraterrestrials in our solar system.

As the inventor of the heliotrope, a device that reflected light to send messages over long distances, Gauss envisioned an array of large mirrors that could be used to flash messages through interplanetary space.

This idea was picked up by the eccentric poet and inventor Charles Cros, who petitioned the French government for funding to build a giant mirror that would use focused sunlight to burn messages into the surface of Mars. Alas, Cros’s request for funding was never granted.

It wasn’t until the advent of wireless communication around the turn of the century that plans for communicating with extraterrestrial intelligence began to take on a more practical form.

Early experiments in long-distance wireless transmission by Marconi and Tesla – both of whom were acutely aware of the implications of their inventions for interplanetary communication – proved that radio communication was a viable method for communicating with intelligent beings on other planets.

In 1932, Karl Jansky serendipitously observed radiation coming from the Milky Way while working at Bell Labs, thereby inaugurating the science of radio astronomy and turning the entire galaxy into fertile hunting grounds for extraterrestrial life.

The first scientific attempt to determine whether we are alone in the galaxy was undertaken by the planetary astronomer Frank Drake at the Green Bank radio observatory in 1960. Over the course of four months, he spent several hours a day observing two nearby stars for any signs of intelligent life.

He came up empty handed, but this is hardly surprising. Had Drake discovered life around these stars, it would either be a remarkable coincidence or suggest the universe is teeming with intelligent life.

Still, Drake recognised the nascent search for extraterrestrial intelligence had a glaring blind spot. If we ever did hear from an extraterrestrial, how would we go about designing a response?

Over the course of the next decade, Drake and some of the world’s pre-eminent scientists devoted considerable intellectual energy to solving this problem. In 1971, researchers from the US and the Soviet Union convened at the Byurakan Observatory in Armenia for the first joint conference on communication with extraterrestrial intelligence and to share their research.

Although scientists on both sides of the iron curtain had been working on this problem separately for years, cold war tensions had made it prohibitively difficult to collaborate.

But as the Soviet astronomer Iosif Shklovsky remarked before the conference, the prospect of communicating with an extraterrestrial intelligence seemed dim if communication between countries was impossible. In this sense, the conference was as much about easing geopolitical tensions on Earth as it was about communicating with ETs.

Our interstellar messages reflect human biases and conventions, and may never be seen by extraterrestrial intelligence

Presiding over the talks was a young Carl Sagan, who fielded interstellar communication proposals from the attendees that were as plentiful as they were fanciful: for example, the extraterrestrial communication proposal floated by the astronomer James Elliot that involved detonating the world’s nuclear arsenal on the far side of the moon. In his analysis of Starfish Prime, a powerful nuclear detonation conducted by the US in space in 1962, he calculated that the x-rays from this explosion could be detected at up to 400 astronomical units, or about 10 times the distance of Pluto from the sun.

While this is not nearly far enough to be detected in another solar system, Elliot suggested that simultaneously detonating all of Earth’s nuclear weapons on the far side of the moon might do the trick.

Based on his estimation of the size of the US and Soviet nuclear stockpiles and an assumption that a device could be developed that would focus the detonation’s resulting x-rays toward a desired target, Elliot calculated that a blast of this magnitude could be detected at up to 190 light years from Earth.

It would be a remarkable way to introduce ourselves, but extraterrestrials would have to be observing Earth at the time of the blast, which Elliot conceded made it a less than practical proposal.

Though a number of other exotic interstellar communication schemes were floated during the Armenia conference, most of the attendees focused on radio waves as a mundane but eminently more practical communication medium.

There were plenty of pragmatic concerns to be addressed when it came to radio transmissions, such as the ideal transmission frequency and choice of stellar targets, but one of the more pressing questions concerned the nature of the message’s content.

Among the various proposals for interstellar messages raised at Byurakan, one especially stands out: Minsky, widely regarded as the father of AI, suggested it would be best to send a cat as our extraterrestrial delegate.

Behind his humour is a serious proposal. During the conference, attendees debated the best way to convey information about life on Earth, such as the existence of cats. A number of attendees argued that images or symbolic messages would probably be the best way to proceed, but Minsky disagreed.

“Instead of sending a very difficult-to-decode educational message and instead of sending a picture of a cat, there is one area in which we can send the cat itself,” Minsky said. “Briefly, the idea is that we can transmit computers.”

In Minsky’s mind, an ideal interstellar message would teach an extraterrestrial how to run computer software that could then teach it about life on Earth. This would allow for a far more energy efficient and information rich message when compared with trying to capture the same information in pictures of symbolic messages.

The future of interstellar messaging will probably be a mixture of state-of-the-art technology and human culture. Just like the golden records attached to the Voyager spacecraft that departed for interstellar space in the 1970s, each interstellar message is a reflection of the culture that created it.

A gold record that was on board the Voyager space probe in 1977. It contained recordings of life and culture on Earth, and the cover had instructions for any extraterrestrial wishing to play it. Photograph: Nasa/Getty Images

In the 1970s, it was a phonograph record filled with everything from 50s rock and roll music to traditional music from Papua New Guinea. More recently, the Sónar messages broadcast from a radar in Norway contained a unique artificial language designed for interstellar communication and short electronic music clips designed by an international collection of musicians.

Tomorrow, our messages will be even more sophisticated. The Seti Institute’s Earthling project, for instance, is amassing a database of sounds submitted by users around the world, which will be electronically remixed to create unique songs that try to capture human music as a gestalt before it is broadcast into space.

In the nearly 50 years since the Byurakan conference, the art and science of interstellar message design has continued to evolve in ways that reflect advances in transmission technology and our understanding of human cognition.

Since we have yet to achieve first contact, humans remain the only animal in the known universe endowed with higher intelligence, which manifests in our ability to wield language, mathematics, and artistic representation.

Our interstellar messages inevitably reflect human biases and conventions, and may never be seen by an extraterrestrial intelligence. But by continuing to explore the problem of interstellar communication, we can learn a lot about what it means to be human in preparation for the day that we discover we’re not alone.